The present invention relates to a color image forming apparatus that can be applied to a color printer, a color copying machine or a color facsimile, and it relates, in particular, to a color image forming apparatus that forms a color image by overlapping multicolor toner images by electrophotography.
In such a color image forming apparatus, development units of four colors (yellow, magenta, cyan and black) usually are used. These development units are contained in a carriage supported rotatably within a perpendicular plane in a main body of the apparatus, so that a photosensitive body of the development unit for each color is moved sequentially between an image forming position and a waiting position, whereby the development units can be switched.
In this type of color image forming apparatus in which a plurality of the development units are contained in the carriage and rotated within the perpendicular plane as described above, it is necessary to provide a mechanism for preventing each of the development units from dropping out of the carriage. In the following, the configuration around a carriage of a conventional color image forming apparatus having such mechanism will be described with reference to FIG. 12.
As shown in FIG. 12, the interior of a carriage 1041 is provided with four carriage reinforcing plates 109 that are arranged radially from a rotation center of the carriage 101 and spaced away from each other by 90xc2x0. These carriage reinforcing plates 109 also serve as partition plates for dividing an inner space of the carriage 101 into four spaces. A development unit 102 is contained in each of these four spaces.
Each of these four spaces in the carriage 101 is provided with a carriage guide groove 105 and a guide pin groove 106 for guiding the development unit 102. The end of the carriage guide groove 105 is formed to be slightly larger than the other portion. Also, near the end of the guide pin groove 106, a unit lock member 107 is provided such that its tip is located inside the guide pin groove 106, and the unit lock member 107 constantly is forced by a unit lock spring 108 toward the guide pin groove 106. On the other hand, each of the development units 102 is provided with a development unit rotating shaft 103 to be guided along the carriage guide groove 105 and a development unit guide pin 104 to be guided along the guide pin groove 106. The development unit rotating shaft 103 has an oval-shaped cross-section. After being inserted in the carriage 101 from above, each of the development units 102 is rotated toward an arrow direction, so that the development unit guide pin 104 advances over the unit lock member 107 and then is locked. At this time, the development unit rotating shaft 103 comes to engage the end of the carriage guide groove 105. The above-described double lock state makes it possible to prevent each of the development units 102 from dropping out of the carriage 101.
However, in the conventional color image forming apparatus described above, because the lock mechanism is provided, two actions are needed for attaching the development unit to the apparatus main body or removing the development unit from the apparatus main body, causing a problem in that the attaching/removing of the development units becomes complicated.
The present invention was made in order to solve the conventional problem mentioned above, and it is an object of the present invention to provide a color image forming apparatus that can prevent a development unit from dropping out of a carriage, without any lock mechanism.
In order to achieve the above-mentioned object, a first configuration of a color image forming apparatus according to the present invention includes a plurality of development units, each development unit having a toner for a different color and a developing member, a carriage for supporting the plurality of development units so as to be attachable/removable with respect to an apparatus main body, a carriage driving system for rotating the carriage so as to move the plurality of development units sequentially and switch them between an image forming position and a waiting position, a unit positioning system for positioning the development unit at a normal position with respect to the apparatus main body in the image forming position, guide rails for restricting a moving track of the development unit during a rotation of the carriage, and a transfer system for transferring a toner image formed by the plurality of development units onto a printing medium. With this first configuration of the color image forming apparatus, since the development unit can be rotated in such a manner as to be held between the carriage and the guide rails, the moving track of the development unit is stabilized. Also, since a lock mechanism or the like for preventing the development unit from dropping out of the carriage becomes unnecessary, the development unit can be attached or removed in a single action when it is located in an upper side of the carriage.
In the first configuration of the color image forming apparatus according to the present invention described above, it is preferable that the guide rails are fixed to left and right side plates of the apparatus main body, and both ends of the development unit are supported by the guide rails. With this preferable example, the guide rails can be formed using relatively small members.
In the first configuration of the color image forming apparatus according to the present invention described above, it is preferable that the guide rails are formed to have an arc shape whose center corresponds to a rotation center of the carriage, and a bisectional point of the arc shape (a point bisecting the arc) of each of the guide rails is located lower than the rotation center of the carriage. With this preferable example, the development unit reliably can be prevented from dropping out.
In the first configuration of the color image forming apparatus according to the present invention described above, it is preferable that at least one of the plurality of development units can be attached to/removed from the apparatus main body when located outside a fan-shape formed by the guide rails and a rotation center of the carriage. With this preferable example, the development unit can be removed only by lifting it up and attached only by dropping it in.
In the first configuration of the color image forming apparatus according to the present invention described above, it is preferable that the development unit does not contact the guide rails when the development unit is positioned in the image forming position by the unit positioning system. With this preferable example, since the development unit does not contact the guide rails in the image forming position, the development unit can be positioned accurately. After the positioning, it also is possible to prevent an external force inhibiting an excellent image formation from being applied to the development unit.
In the first configuration of the color image forming apparatus according to the present invention described above, it is preferable that each of the plurality of development units integrally includes a photosensitive body having a surface on which a static latent image is formed, and development unit guide portions that slide in contact with the guide rails during the rotation of the carriage are provided on left and right ends of the photosensitive body. With this preferable example, while avoiding the contact of the exposed photosensitive body with the guide rails and other components on the main body side, it is possible to restrict the moving track of the development units reliably during the rotation of the carriage. In this case, it is preferable that the development unit guide portions are provided on a line connecting a rotation center of the carriage and a center of the photosensitive body. With this preferable example, it is possible to minimize the contact length along which the photosensitive body slides over the intermediate transfer belt during the rotation of the carriage (an unprintable region). Furthermore, in this case, it is preferable that a concave portion is provided in a part of the guide rails so that the development unit guide portions do not contact the guide rails when the development unit is positioned in the image forming position by the unit positioning system. With this preferable example, since the development unit can be prevented from contacting the guide rails in the image forming position, the development unit can be positioned accurately. Also, it is possible to prevent an external force inhibiting an excellent image formation from being applied to the development unit.
Furthermore, a second configuration of a color image forming apparatus according to the present invention includes a plurality of development units, each development unit having a toner for a different color and a developing member, a carriage for supporting the plurality of development units so as to be attachable/removable with respect to an apparatus main body, a carriage driving system for rotating the carriage so as to move the plurality of development units sequentially and switch them between an image forming position and a waiting position, a unit positioning system for positioning the development unit at a normal position with respect to the apparatus main body in the image forming position, a carriage positioning system for positioning the carriage at a normal position with respect to the apparatus main body, and a transfer system for transferring a toner image formed by the plurality of development units onto a printing medium. With this second configuration of the color image forming apparatus, even when a rotational force is applied to the carriage during a printing operation, the carriage can be held in an accurate position. In addition, since the positioning mechanism is provided independently of the carriage driving mechanism, a positional accuracy of the stopping position required for the carriage driving mechanism is eased.
In the second configuration of the color image forming apparatus according to the present invention described above, it is preferable that, when the development unit and the carriage are positioned in the image forming position, the development unit other than the positioned development unit can be attached to/removed from the apparatus main body. With this preferable example, the attachment/removal of the development unit and the image formation are possible in one carriage stopping position, eliminating the need for providing another carriage stopping position for the attachment/removal of the development unit, allowing a simple control. In addition, the attachment/removal of the development unit is not prevented by an accompanying rotation of the carriage. In this case, it is preferable that, in a waiting state of the apparatus, the carriage is positioned and fixed to the normal position with respect to the apparatus main body. With this preferable example, simply by opening an upper cover of the apparatus in the waiting state, the development unit can be replaced. In addition, there is no concern of rotating the carriage by mistake when opening the upper cover of the apparatus in the waiting state.
In the second configuration of the color image forming apparatus according to the present invention described above, it is preferable that the unit positioning system and the carriage positioning system both include a pin reciprocating in a direction parallel to a rotation axis of the carriage. With this preferable example, two members, namely, the development unit and the carriage can be positioned by a single driving source and transmitting members, achieving a simple configuration.
Moreover, a third configuration of a color image forming apparatus according to the present invention includes a plurality of development units, each development unit having a toner for a different color and a developing member, a carriage for supporting the plurality of development units so as to be attachable/removable with respect to an apparatus main body, a carriage driving system for rotating the carriage so as to move the plurality of development units sequentially and switch them between an image forming position and a waiting position, a transfer system for transferring a toner image formed by the plurality of development units onto a printing medium, a carriage position detecting portion formed integrally with the carriage in an outermost peripheral portion of one of the left and right ends of the carriage, a position detection sensor for detecting the carriage position detecting portion, and a unit detecting portion formed integrally with the development unit so as to be located at substantially the same distance from a rotation center of the carriage as the carriage position detecting portion. With this third configuration of the color image forming apparatus, since the position detecting portions are formed integrally with the carriage and the development unit, it is possible to detect the position of the carriage and the presence of the development unit using a single sensor without an additional component.
In the third configuration of the color image forming apparatus according to the present invention described above, it is preferable that the number of the carriage position detecting portions is the same as that of the development units supported by the carriage, and one of the carriage position detecting portions has a different shape from the other carriage position detecting portions. With this preferable example, it is possible to detect an origin of one rotation of the carriage by the single position detection sensor, allowing a color detection.
Also, in the third configuration of the color image forming apparatus according to the present invention described above, it is preferable that the unit detecting portion has a different shape from the carriage position detecting portion. With this preferable example, it is possible to discriminate between the detection of the carriage position and that of the presence of the development unit.
Also, in the third configuration of the color image forming apparatus according to the present invention described above, it is preferable that a plurality of the unit detecting portions can be provided for each one of the development units. With this preferable example, it is possible to detect information of the development unit, for example, a difference of a contained toner and photosensitive body sensitivity and that of an intended use.
Also, a fourth configuration of a color image forming apparatus according to the present invention includes a plurality of development units, each development unit having a toner for a different color and a developing member, a carriage for supporting the plurality of development units so as to be attachable/removable with respect to an apparatus main body, a carriage driving system for rotating the carriage so as to move the plurality of development units sequentially and switch them between an image forming position and a waiting position, and a transfer system for transferring a toner image formed by the plurality of development units onto a printing medium. The carriage includes left and right carriage side plates that can position the development unit substantially and a hollow pipe member that joins the left and right carriage side plates, and the pipe member includes two-divided sheet-like pipe element members. With this fourth configuration of the color image forming apparatus, the hollow pipe member is two-divided, and an inexpensive pipe member can be achieved.
In the fourth configuration of the color image forming apparatus according to the present invention described above, it is preferable that one of the two-divided pipe element members has at least one convex portion provided perpendicularly to a rotation axis of the carriage, and the other has a concave portion that fits the convex portion. With this preferable example, when the pipe member is twisted, these two pipe element members can be prevented from sliding in a direction parallel to the rotation axis of the carriage, thereby improving the torsional stiffness of the pipe member considerably.
Also, in the fourth configuration of the color image forming apparatus according to the present invention described above, it is preferable that the pipe member has a polygonal cross-section perpendicular to a rotation axis of the carriage. With this preferable example, it is possible to achieve a further inexpensive hollow pipe member using the pipe element members, which can be manufactured in an inexpensive manner by a regular press working.
Furthermore, a fifth configuration of a color image forming apparatus according to the present invention includes a plurality of development units, each development unit having a toner for a different color and a developing member, a photosensitive body, a carriage for supporting the plurality of development units so as to be attachable/removable with respect to an apparatus main body, a carriage driving system for rotating the carriage so as to move the plurality of development units sequentially and switch them between an image forming position and a waiting position, an exposing system for exposing the photosensitive body, and a transfer system for transferring a toner image formed on the photosensitive body onto a printing medium. The exposing system is a laser beam scanner whose light source is a semiconductor laser, and a part of or all of an image forming lens and a reflecting mirror that serve as element members of the laser beam scanner are arranged inside a rotational moving track of the plurality of development units. With this fifth configuration of the color image forming apparatus, a further compact apparatus can be achieved.
In the fifth configuration of the color image forming apparatus according to the present invention described above, it is preferable to further include carriage rotating shaft members that are fixed to left and right side plates of the apparatus main body and support a rotation axis of the carriage, in which the reflecting mirror is fixed to the carriage rotating shaft members at a position substantially matching the rotation axis of the carriage. With this preferable example, it is possible to minimize an error of the attachment position of the reflecting mirror. In this case, it is preferable that the carriage rotating shaft members are attached rotatably with respect to the left and right side plates of the apparatus main body. With this preferable example, the angle of the reflecting mirror easily can be adjusted simply by rotating the carriage rotating shaft members. Consequently, it is not necessary to add another component for the angle adjustment, contributing to a cost reduction.
Moreover, a sixth configuration of a color image forming apparatus according to the present invention includes a plurality of development units, each development unit having a toner for a different color and a developing member, a carriage for supporting the plurality of development units so as to be attachable/removable with respect to an apparatus main body, a carriage driving system for rotating the carriage so as to move the plurality of development units sequentially and switch them between an image forming position and a waiting position, and a transfer system for transferring a toner image formed by the plurality of development units onto a printing medium. The development unit is supported inside the carriage so as to be capable of reciprocating in a direction parallel to a rotation axis of the carriage. With this sixth configuration of the color image forming apparatus, since the development unit is capable of reciprocating in the carriage, a part of the unit positioning system, which positions the development unit with respect to the apparatus main body in the image forming position, can be supported rigidly in the apparatus main body. This makes it possible to improve the positioning accuracy and constitute the apparatus at low cost.
In the sixth configuration of the color image forming apparatus according to the present invention described above, it is preferable to further include a unit feeder terminal that is provided on an end face of the development unit perpendicular to the rotation axis of the carriage, for supplying a voltage or an electric current necessary for an image formation to the development unit, and a main body feeder terminal that is provided in the apparatus main body, for supplying electricity by contacting the unit feeder terminal directly when the development unit is in the image forming position. With this preferable example, since the development unit is capable of reciprocating in a direction of the rotation axis of the carriage, the unit feeder terminal and the main body feeder terminal do not contact each other or contact with a slight contact pressure during the rotation of the carriage. Therefore, it is possible to suppress a change in characteristics of the terminal surface caused by abrasion and noise generation caused by friction. In addition, since the unit feeder terminal is brought into contact with the main body feeder terminal while being connected with the positioning system of the development unit, it is possible to achieve the connection of the both terminals without any driving source exclusively for this purpose.
In the above-described preferable example, it is further preferable to include a unit positioning system for positioning the development unit at a normal position with respect to the apparatus main body in the image forming position, the unit positioning system including a pair of unit positioning pins that are capable of moving in the direction parallel to the rotation axis of the carriage and restrict a position of the development unit in this direction, in which the position of the development unit is restricted substantially using the unit positioning pin on a side of the main body feeder terminal, and then the position of the development unit is restricted using the unit positioning pin on the other side. With this preferable example, when positioning the development unit, it is possible to minimize the amount the development unit moves in the direction of the rotation axis of the carriage, thereby preventing deformation or breakage of the main body feeder terminal and abrasion of the unit feeder terminal and the main body feeder terminal because of the sliding of these terminals. Furthermore, by the movement of the unit positioning pin on the other side, restricting the position of the development unit and connecting the main body feeder terminal and the unit feeder terminal are completed at the same time, allowing an efficient operation with a simple configuration.
In addition, a seventh configuration of a color image forming apparatus according to the present invention includes a plurality of development units, each development unit having a toner for a different color, a developing member and a unit feeder terminal for supplying a voltage or an electric current necessary for an image formation, a carriage for supporting the plurality of development units so as to be attachable/removable with respect to an apparatus main body, a carriage driving system for rotating the carriage so as to move the plurality of development units sequentially and switch them between an image forming position and a waiting position, and a transfer system for transferring a toner image formed by the plurality of development units onto a printing medium. The apparatus includes an charge eliminating member for eliminating a residual electric charge in the development unit by contacting the unit feeder terminal directly when the development unit is located out of the image forming position. With this seventh configuration of the color image forming apparatus, when the development unit rotates after an image formation is finished, so that the unit feeder terminal contacts the main body feeder terminal in the image forming position again, it is possible to suppress the noise generation caused by the discharge of the residual electric charge in the development unit to the main body feeder terminal.
In the seventh configuration of the color image forming apparatus according to the present invention described above, it is preferable that the charge eliminating member is made of a flexible material with a resistance value of 1 kxcexa9 to 10 Mxcexa9 and fixed to the apparatus main body so as to be grounded. With this preferable example, it is possible to eliminate electricity while avoiding a sudden discharge.